84 



wilhoul loiicliing the shell. In this way sufficient embryos 

 are colleeled on :i sterile watchglass. The embryos are wa- 

 shed wilii a iilllf l{in<^ei-s solution which is drawn off 

 again will a pipette. Then the embryos are cut up with 

 a pair ol small curved scissors, until a line pulp is obtained 

 and then this is j)lace(l in small narrow (5 m. m. in dia- 

 meter lubes \)\ means of a pipette and centrifuged for 

 ten minutes. The supernatant fluid in these tubes is then 

 ready for use. The fluid is a little opaque and rather mucous. 

 I have observed that the embryonic tissue juice obtained 

 in this way has a much more activating power than if the 

 embryos were ground with sand or kieselgur in a mortar. 

 It is always advisable to draw off the tissue juice from 

 I he pulp and keep it sepai'ately in the refrigerator. It keeps 

 betlei" and the hydrogen ion concentration keeps more con- 

 stant for a longer period of time. The tissue juice loses its 

 activating power and becomes rather acid if the tissue 

 pulp is allowed to remain with the juice. Usually the tissue 

 juice is prepared fresh every time it is to be used. 



MAKING THE CULTURES. 



The apparatus necessary for the complete culture work 

 is the following: 



The plasma in paraffin-coated tubes 



The embryonic tissue juice 



Ringer's solution 



Tyrodes solution 



Rubber nipples for the pipettes (autoclaved in water) 



Pasteur pipettes 



Centrifuge tubes 



Big glass dishes, containing the hollow slides 



Coverglasses 



Cataract knives 



Steel needle on a shaft 



Coverglass forceps 



Iris forceps 



